Sexual Selection Flashcards
How to distinguish between the two sexes across sexually reproducing species?
Gamete size - male gametes/sperm are a lot smaller than female gametes/eggs (typically)
Sexual dimorphism
Phenotypic differences between males and females of the same species (peacocks, lions)
Sexual selection
Differences in fitness caused by differences in mating success among individuals of the same sex, leads to evolution of traits that increase mating success, explains traits that don’t make sense I’m the context of other aspects of the environment (social environment is powerful)
Reproductive investment
Males - sperm are cheap and less parental care is provided
Females - eggs are more expensive and more parental care provided
Limits on reproductive success
Males - limited by number of females acquired as mates
Females - limited by resources to produce young
Greater variation in naïf success typically
Males (fail to mate vs how many mates found)
Competes for mates
Males typically - invest less time and effort in offspring
Choosy sex
Females typically - invest more time and effort
Stronger sexual selection
Males - compete with others for females (armaments) or attract females (ornaments)
Intrasexual selection
Male-male competition, evolution of male traits (armaments) associated with combat, sperm competition and infanticide
Intersexual selection
Female choice, evolution of male traits (ornaments) associated with good genes, simulations of female sensory biases and sexy sons/run away selection
Male combat traits
Leads to evolution of traits for aggressive interactions with other males one access to females
Sperm competition
Competition between males that have mated with the same female to determine whose sperm will fertilize the eggs, requires multiple mating by females and internal fertilization
Sperm competition traits
- Transfer lots of sperm or large sperm
- Remove, displace, destroy sperm of other males
- Produce a copulatory plug, guard female
Infanticide
Kill off infants of previous males when a new male wins control of an area/group of females so that females will be ready to copulate more rapidly and produce offspring of the new males
Male lions and infanticide
Removes competitors genes, females in pride ready to mate sooner
Female choice traits
Direct benefits (parental care, resources), good genes, traits that are honest indicators of males having better genetic quality
Direct benefits from female choice
Parental care (strength and protection), resources (food)
Explanations why female choice may not always be correlated with direct benefits
Females choose males with traits that are honest indicators of their genetic quality (good genes), sensory bias, sexy sons
Good genes
Males that are honest indicators of their genetic quality
Prediction: offspring of males with preferred traits are more likely I survive/thrive
Runaway sexual selection or sexy sons
Females choose males that are attractive in order to produce attractive sons
How preferences evolve and why prefer them in the first place?
- Some females prefer a particular trait
- Males with trait have slightly higher fitness thus sons inherit sexy trait and daughters inherit preference for sexy trait, more females then prefer trait and males have even higher fitness with trait (snowball effect)
Genetic drift of preference allele, good genes and sensory bias
Female sensory bias
Females choose males with traits that exploit their pre-existing sensory biases
Prediction: preferred male traits resemble other cues that females respond to in the environment
Multiple forms of sexual selection?
Sexual selection mechanisms are not mutually exclusive and can work together
